xref: /illumos-gate/usr/src/lib/libm/common/Q/ilogbl.c (revision ddc0e0b5)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 
22 /*
23  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
24  */
25 /*
26  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
27  * Use is subject to license terms.
28  */
29 
30 #pragma weak __ilogbl = ilogbl
31 
32 #include "libm.h"
33 #include "xpg6.h"	/* __xpg6 */
34 
35 #if defined(__sparc)
36 #define	ISNORMALL(k, x)	(k != 0x7fff)			/* assuming k != 0 */
37 #define	X86PDNRM(k, x)
38 #define	XSCALE_OFFSET	0x406f				/* 0x3fff + 112 */
39 static const long double xscale = 5192296858534827628530496329220096.0L;
40 								/* 2^112 */
41 #elif defined(__x86)
42 /*
43  * if pseudo-denormal, replace by the equivalent normal
44  */
45 #define	X86PDNRM(k, x)	if (k == 0 && (((int *) &x)[1] & 0x80000000) != 0) \
46 				((int *) &x)[2] |= k = 1
47 #if defined(HANDLE_UNSUPPORTED)				/* assuming k != 0 */
48 #define	ISNORMALL(k, x)	(k != 0x7fff && (((int *) &x)[1] & 0x80000000) != 0)
49 #else
50 #define	ISNORMALL(k, x)	(k != 0x7fff)
51 #endif
52 #define	XSCALE_OFFSET	0x403e				/* 0x3fff + 63 */
53 static const long double xscale = 9223372036854775808.0L;	/* 2^63 */
54 #endif
55 
56 static int
raise_invalid(int v)57 raise_invalid(int v) {	/* SUSv3 requires ilogbl(0,+/-Inf,NaN) raise invalid */
58 #ifndef lint
59 	if ((__xpg6 & _C99SUSv3_ilogb_0InfNaN_raises_invalid) != 0) {
60 		static const double zero = 0.0;
61 		volatile double dummy;
62 
63 		dummy = zero / zero;
64 	}
65 #endif
66 	return (v);
67 }
68 
69 int
ilogbl(long double x)70 ilogbl(long double x) {
71 	int k = XBIASED_EXP(x);
72 
73 	X86PDNRM(k, x);
74 	if (k == 0) {
75 		if (ISZEROL(x))
76 			return (raise_invalid(0x80000001));
77 		else {
78 			x *= xscale;		/* scale up by 2^112 or 2^63 */
79 			return (XBIASED_EXP(x) - XSCALE_OFFSET);
80 		}
81 	} else if (ISNORMALL(k, x))
82 		return (k - 0x3fff);
83 	else
84 		return (raise_invalid(0x7fffffff));
85 }
86